Development of the IEEE 802.11ah wireless system is progressing to address many different deployments or use cases for which earlier versions of wireless local area network (WLAN) specifications are not fully suitable. See for example document IEEE 802.11-11/0457r0 entitled POTENTIAL COMPROMISE FOR 802.11 AH USE CASE DOCUMENT by Rolf de Vegt, Qualcomm, March 2011. One such use case is a Smart Grid—Meter to Pole arrangement where the different stations are each associated with an electrical distribution or transmission point and wirelessly report various parameters of the electrical point they sense. In this case the single AP (access point) should be able to support several thousands of stations (STAs), where each sensor is associated with a STA to transmit its sensing data and receive any control information. Other use cases include environmental monitoring sensors; agriculture monitoring sensor systems in support of crops and livestock; industrial process sensors around large facilities such as petroleum refineries, steel smelters and pharmaceutical campuses; indoor healthcare monitoring such as in hospitals, homes and eldercare facilities; and others.
This wide variety of use cases leads to quite different assumptions for them. In some the stations (STAs) are assumed to be fixed in location while in others the STAs can be mobile. Some use cases will entail a low volume of data sent infrequently and where latency is not a major concern, whereas others may need to support higher data volumes and require low latency when data needs to be sent. One aspect many of these use cases reflects is the need to support a large number of STAs. When a large number of sensors/devices are associated with an AP, grouping of STAs is recognized as a means to control channel access, reduce collisions, and save energy.
There have been different proposals already for grouping stations. For example, co-owned UK Patent Application No. GB1119210.1 (filed on Nov. 7, 2011) provides that a STA's group assignment can be based on the device's MAC (Media Access Control) address or the assigned device identity such as the Association Identifier (AID). A STA belonging to a group may decide that its performance is not satisfactory and may request to change its group by proposing to the AP one or more different groups. The AP will either reject the STA's proposal or accept it by specifying the best group to be joined. In one embodiment the STA itself senses the potential groups it can join and identifies its best preference to the AP, and in another the STA may not have information about the potential groups to join so it indicates a performance indication such as a traffic rate requirement in its request to AP.
Another grouping concept is set forth in co-owned UK Patent Application No. GB1204209.9 (filed on Mar. 9, 2012). In that proposal each STA listens to the channel and to the interference that it experiences in each group, and the STA selects the group to join which is the group in which it has the best performance/least interference. Alternatively a STA may choose a group to join at random.
In both those co-owned UK patent applications the number of groups available and the assignment of STAs to groups is maintained by the AP. Performance is improved in both cases due to the group-wise restriction of which STAs can contend for channel access at any given time and the subsequent decrease in the number of collisions. Those concepts are effective grouping techniques and these teachings detail yet another way for assigning STAs to one of several groups under a single AP.